Emission control devices such as catalytic converters achieve higher emission reduction after reaching a predetermined operating temperature, referred to as light-off temperature. During engine cold-start conditions, emission control devices may be operated at temperatures below their light-off temperature. Engine cold-start emissions released before the emission control device has reached its light-off temperature may lower vehicle exhaust quality, and contribute to a large percentage of the total exhaust emissions. Accordingly, various approaches are focused on reducing cold-start emissions.
One example approach described in U.S. Pat. No. 8,464,542 involves reducing a level of wet exhaust reaching the catalytic converter by utilizing a system to trap liquid exhaust. Therein, engine exhaust is condensed to form liquid exhaust, and the liquid exhaust is stored in a trap. After the catalyst has reached a light-off temperature, the liquid exhaust is released back from the trap into the exhaust system. However, the inventors herein have recognized potential issues with such an approach. For example, addition of a trap to the exhaust system may lead to increased design and manufacturing costs. In addition to the trap, components such as a baffle may be included in the exhaust system to condense exhaust, which may also contribute to production costs. Further, the trapped liquid exhaust may not be released completely during operation of the vehicle. As a result, liquid exhaust may accumulate in the trap over time leading to failure of the trap system. Therefore, additional sensors and connections may be required to constantly monitor the trap system, further increasing the design complexity and production cost.
In one example, some of the above issues may be at least partially addressed by a system, comprising: an exhaust passage; a restriction valve positioned upstream of an emission control device and downstream of a turbine and a wastegate in the exhaust passage opposite an oxygen sensor; and a pre-catalyst exhaust recycling passage coupled to the exhaust passage via the restriction valve to flow engine exhaust into an intake passage upstream of a compressor inlet during cold-start conditions.
As an example, during an engine cold-start, while a temperature of an emission control device, such as a catalytic converter is below a threshold temperature (e.g. light-off temperature), a restriction valve may be opened to block a portion of engine exhaust in the exhaust passage upstream of the catalytic converter. The blocked portion of exhaust may be not flow through the catalytic converter and may be diverted to a compressor inlet via a pre-catalyst exhaust recycling passage connecting the exhaust passage upstream of the catalytic converter and downstream of the turbine with the intake passage upstream of the compressor. Further, the restriction valve may not completely block an entire amount of exhaust in the exhaust passage. A remaining portion of the exhaust not blocked by the restriction valve may flow through the catalytic converter to enable heating of the catalyst. Upon the temperature of the catalytic converter reaching the threshold temperature, the restriction valve may be closed to stop recycling the exhaust via the pre-catalyst exhaust recycling passage, and the entire amount of exhaust may be allowed to flow through the catalytic converter.
In this way, the restriction valve may be utilized to reduce an amount of engine exhaust flowing through the catalytic converter when the catalyst temperature is below its light-off temperature. By reducing the amount of exhaust flowing through the catalyst, cold-start emissions may be reduced.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.